Dental Hypotheses

: 2019  |  Volume : 10  |  Issue : 1  |  Page : 9--13

Effect of Furcation Perforation Size on Fracture Resistance of Mandibular First Molar

Ladan Jamshidy1, Zahra Amirkhani1, Roohollah Sharifi2,  
1 Department of Prosthodontics, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran
2 Department of Endodontics, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran

Correspondence Address:
Roohollah Sharifi
Department of Endodontics, Shariati street, Kemanshah province, Kermanshah


Introduction: Which were weakening furcation area can reduce tooth strength against fracture. The present study assessed fracture resistance in the mandibular first molars perforated at furcation area and sealed with mineral trioxide aggregate (MTA). This study was aimed to investigate the effect of furcation perforation size on fracture resistance in first mandibular molar teeth. Material and Methods: The cervical region of 50 mandibular first molars were cut at cenentum enamel junction level. After root preparation and obturation, the samples were randomly classified into five groups: group 1:1 mm perforation, reconstructed with MTA; group 2:1 mm perforation, without repair, with wax filling; group 3:2 mm perforation, reconstructed with MTA; group 4:2 mm perforation, without repair, with wax filling; and group 5: without perforation. The compressive force breaking each sample was recorded. Data were subjected to SPSS-20 software to analyze by Kolmogorov–Smirnov test, two-way ANOVA, and independent samples t-test. Results: Furcation perforation and MTA had no significant effect on the force at the break point; no significant difference between 1 and 2 mm perforations either MTA restored or wax filled was registered. No significant difference in mean force at the break point between groups with or without perforation was observed. Conclusions: One and 2 mm furcation perforation does not reduce the fracture resistance. MTA in 1 or 2 mm perforations does not increase the fracture resistance.

How to cite this article:
Jamshidy L, Amirkhani Z, Sharifi R. Effect of Furcation Perforation Size on Fracture Resistance of Mandibular First Molar.Dent Hypotheses 2019;10:9-13

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Jamshidy L, Amirkhani Z, Sharifi R. Effect of Furcation Perforation Size on Fracture Resistance of Mandibular First Molar. Dent Hypotheses [serial online] 2019 [cited 2019 Jul 23 ];10:9-13
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Root canal perforation is defined as a communication between the root canal system and the surrounding periodontal tissues.[1] This communication can be caused by various reasons such as caries, resorption, or iatrogenic factors.[2] It has different prognoses depending on the location and size of perforation.[3] Perforation causes mechanical weakening of the root, direct impairment of the root structure, and periodontal trauma. It also creates a potential route for microorganisms to enter the root canal.[4] Furcation perforation has a higher risk for the loss of periodontal attachment and bone resorption due to closeness to gingival sulcus.[5],[6],[7] An ideal restorative material for perforation must provide an adequate sealing, be biocompatible, have stable dimensions, be insoluble and radiopaque, and be easily placed in the root canal.[8],[9] For example, the main compounds of mineral trioxide aggregate (MTA) that functions as a candidate for closing the communication between root canal and periodontal tissues[10],[11] include tricalcium silicate, tricalcium aluminate, dicalcium silicate, calcium sulfate dehydrate, and bismuth oxide; its pH after hardening is 12.5, which is the same as that of calcium hydroxide. Exclusive properties like high strength at the presence of humidity,[12] appropriate biocompatibility,[9] reduction of microleakage and bacterial penetration, low toxicity, induction of cement formation, and increased survival of treatment are some other benefits of this material.[10],[11],[12],[13],[14] The furcation area is considered as a strong region owing to being located in the connection center of two or three roots. Therefore, any weakening of this area, including furcation perforation, can exert a remarkable impact on the reduction of tooth strength against fracture during function.[15],[16] It has been shown that MTA has a weakening effect on dentin probably due to the fracture of structural proteins owing to their alkaline properties.[17] In clinical applications such as furcation perforation when MTA is under the influence of functional force, its strength can be a significant factor.[18]

This study aimed to investigate the effect of furcation perforation on the fracture strength of mandibular first molars. Our results provide clinical criteria for the clinicians to anticipate the reduced resistance against fracture.

 Materials and Methods

Fifty mandibular first molars were considered (10 teeth in five group)


α = 0.05, and 1- β = 90% (power) [19]

The samples were randomly chosen through convenience sampling. Examination of all the teeth using a stereomicroscope (SZM-2, OPTIKA, Ponteranica, Italy) at 4× magnification confirmed that all the teeth have separate tools, no caries and previous restoration, and were without crack and fracture at furcation area. Immersing the samples in 5.25% sodium hypochlorite for 1 h removed the soft tissue and debridements; then they were kept in 0.9% physiologic serum at room temperature.[20]

At the next stage, access cavity was prepared for each tooth, and the cervical margin at CEJ was cut perpendicular to dental longitudinal axis by a diamond bur (Diamond discs 22 mm, Zogear, Shanghai, China) under coolant.[21] The samples were prepared by manual files no. 8, no. 10, and no. 15 (VDW-dental, München, Germany). Then, the teeth were cleaned by Mtwo rotary file (VDW-dental, München, Germany) and files no. 15 (5% taper), no. 2 (6% taper), and no. 52 (6% taper). The samples were filled with gutta-percha (Gapadent, TianJin, P.R. China), and the sealer (AH26, silverfree, Dentsply, Detrey, Germany) was obturated by lateral obturation method. Using a carbide rotary bur, two perforations, one with 1 mm diameter (Teeskavan, Iran, 012.801) and other with 2 mm diameter (Teeskavan, Iran, 016.801), were created in the midpoint of the mesial and distal furcations perpendicular to the longitudinal axis of the teeth in groups 1 to 4. The area under the furcation between the mesial and distal roots was sealed with acryl. Then, the tooth surroundings were covered with a thin layer of 1.5 to 2-mm-thick wax and fixed in 20 × 20 × 25 acrylic blocks parallel to the longitudinal axis,[22] so that a distance of 2 mm was maintained between the CEJ and resin block surface.[23]

The samples were randomly divided into five groups (each group with 10 samples):Group 1. Teeth with 1 mm perforation and repaired with MTAGroup 2. Teeth with 1 mm perforation without repairGroup 3. Teeth with 2 mm perforation and repaired with MTAGroup 4. Teeth with 2 mm perforation without repairGroup 5. Teeth without perforation

According to Salehimehr et al.,[24] the perforations at groups 1 and 3 were repaired with MTA Angelus (MTA ANGELUS, Londrina, PR, Brazil), covered with wet cotton, and dressed with Cavit (Cavisol, Golchadent, Tehran, Iran). The perforations of groups 2 and 4 were filled with wax and dressed with Cavit. The access cavity of group 5 was filled with Cavit up to the CEJ surface. After preparation, the samples were kept in normal saline at room temperature.[25] After 2 months, they were placed in a Universal Testing Machine (STM-20, Santam, Iran) under a compressive force of 1 mm/min.[26] The vertical force was applied by a cylindrical stainless steel bar with a circular cross-section and 10 mm diameter. The cross-section of the bar covered the access cavity surroundings at the cervical margin, and force was consistently applied by the machine until fracture occurred. The force required for the fracture of each sample was recorded in Newton and the obtained values were subjected to statistical analysis.

Data were analyzed by SPSS-20 software (SPSS Inc., Chicago, IL, USA) using descriptive and inferential statistics. For inferential statisics, normality of data was determined by Kolmogorov–Smirnov test. Given the normality of the data, two-way ANOVA was run to analyze the effect of MTA and furcation perforation on the amount of force. Also, independent samples t-test was used for pair comparisons. P < 0.05 was considered significant.


The mean thickness of the cross-section was 73.1 mm in group 1, 72.8 mm in group 2, 72.9 mm in group 3, 82.8 mm in group 4, and 69.5 mm in group 5. The mean length of the samples was 14.9 mm in group 1, 15.3 mm in group 2, 14.3 mm in group 3, 15.3 mm in group 4, and 14.7 mm in group 5. The mean force at the break and peak points in the groups followed a normal distribution (P > 0.6).

The highest mean ± standard error fracture force (2814.21 ± 21N) was found for group 5 (without furcation perforation), and the lowest one (2048.48 ± 1113.23N) was reported for group 4 (2 mm perforation filled with wax). The mean ± standard deviation (SD) fracture forces of the groups 1, 2, and 3 were 2426.11 ± 1214.83N, 2233.34 ± 1252.05N, and 2236.19 ± 1102.3N, respectively [Table 1].{Table 1}

The findings showed that furcation perforation and MTA had no significant effect on the fracture force at break point (two-way ANOVA, P > 0.05).

The highest mean ± SD peak force (2858.87 ± 2225.71N) before fracture was observed in group 5 and the lowest level (2060.83 ± 1129.98N) was found in group 4. The mean ± SD peak forces of the groups 1, 2, and 3 were 2464.86 ± 1271.74N, 2244.53 ± 1256.44N, and 2244.82 ± 1103.44N, respectively [Table 2].{Table 2}

The mean forces (N) at break point with perforation (2236.03) and without perforation (2814.21) are presented in [Table 3]. No significant difference was between the mean forces at break point with and without perforation (independent sample t-test, P > 0.05).{Table 3}

The mean forces (N) at peak point with perforation (2253.76) and without perforation (2858.87) are shown in [Table 4], indicating no significant difference between the mean forces at peak point with and without perforation (independent sample t-test, P > 0.05).{Table 4}


Furcation area is a significant site involved in the strength of tooth, and furcation perforation plays an important role in resistance against fracture during function.[27],[28],[29],[30],[31] The restorative materials used for sealing the furcation area have to fulfill the functional requirements of the teeth, including mechanical forces applied on the perforation area.[21],[30] Accordingly, the present study was designed to compare the amount of force required for fracturing perforated and imperforated teeth at furcation area. Although the healthy teeth needed approximately 600N more fracture force than the perforated teeth,[13] no significant difference was observed between the perforated and unperforated teeth in mean forces at break point. The perforation size is among the factors that affects successful perforation repairment. Small perforations promote the direct and immediate restorations,[32] reducing the chance of periodontal failure and epithelial proliferation at perforation area.[33] In a situation that the restorative material contacts largely with periodontium, the perforation prognosis becomes unclear because of probable inflammatory stimulation that can propagate into the adjacent tissues. Also, marginal adaptation is reduced with increase of the defective area.[34] The effect of furcation perforation size on the efficacy of restorative material is still undetermined. Some studies argued that tooth size in relation to perforation size directly affects the prognosis,[31],[33],[35] whereas some others reported no association between the two variables.[36]

Analysis of dental materials has shown that the materials with same elasticity as dentin can reinforce the weak roots.[37] On the contrary, the samples obturated with gutta-percha, MTA, and calcium phosphate have a higher fracture strength than unobturated samples.[38] Although MTA is the material of choice for furcation perforation repairment,[14] some studies have indicated that MTA weakens the dentin.[17]

The studies conducted on the effect of MTA on the fracture strength have reported contradictory results. Bortoluzzi et al.[39] showed that use of MTA and metal post significantly increased fracture resistant in bovine immature teeth. Compared to our study, the difference may be attributable to simultaneous use of metal post and MTA, obturation of root canal length with MTA (unlike our study in which only furcation perforation was filled with MTA), and cutting the 12-mm apical root as close to the CEJ. However, the root was untouched up to apical region in our study. Milani et al.[40] reported a higher fracture strength in MTA obturation group. Comparatively, using immature maxillary incisors and a different method, in which all the root length was filled with MTA and the root was cut 9 mm lower than CEJ, may be presumptive causes of the difference; the roots were healthy in our study.In the terms of causality of strength change, White et al.[17] argued that the reduction may be related to the structural proteins created by the alkaline properties of restorative materials like MTA. However, Sahebi et al.[41] believed that fracture of structural proteins causes the root strength to decrease.

Our results showed that the fracture strength of the samples with 1 mm perforation in MTA perforation group was about 200N higher than that of 1 mm perforation group obturated with wax. However, furcation perforation and MTA had no significant effect on the force at break point (P > 0.05). Moreover, despite 200N difference in 2-mm perforation groups, there was no significant difference between the MTA group and the wax group (P > 0.05). This insignificant difference might be due to the low sample size, patients’ age, type of occlusion in the teeth once present in the jaw arch, and diet of these samples as type of occlusion and age affect the dentinogenesis and calcification and consequently the tooth strength.[42] Moreover, MTA Angelus did not increase the tooth strength in 1 or 2 mm perforations. As the roots were not cut and root treatment stages and perforation repair were reconstructed similar to the clinical conditions, the strength is probably closer to in vivo conditions.

Gathering healthy first mandibular molar teeth of same forms and sizes was the great challenge of our study. Nonetheless, further studies would be recommended to include a relatively large healthy group with no endodontic treatment. Also, it is needed to assess the variability trend of the fracture resistance at different times in a larger sample size.

The present study leads us to the conclusion that furcation perforation did not decrease the tooth strength and repairing the perforations with MTA Angelus did not increase the tooth strength.

Financial support and sponsorship

The current research was supported and ethically approved by the Research Council of the Kermanshah University of Medical Sciences, Kermanshah, Iran (96361).Conflicts of interest

There are no conflicts of interest.


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